Such foundation structures which are based on a jacket construction are used in particular in the installation of wind power installations in offshore regions involving a great depth of water. The jacket construction has increased water permeability in comparison with usual monopile constructions, so that the loadings on the offshore foundation structure, that are caused by the flow of water, are reduced.
It has further already been shown that the installation of jacket-based offshore foundation structures can be implemented in such a way as to produce substantially lower levels of emissions. Jacket constructions permit anchorage to the bed of the body of water with a plurality of driven piles. Driving in a plurality of small driven piles into the bed of the body of water can be carried out with a substantially lower level of emissions than driving in large monopile anchorings.
Because wind power installations are continuously increasing in size the demands made on the offshore foundation structures in regard to their load-bearing capability are also increasing.
Furthermore considerable dynamic forces are also applied by the tower of the wind power installation to the offshore foundation structure which has to support them in relation to the bed of the body of water. In order to be able to use wind power installations in offshore areas involving high wind strengths there is also regularly a need for foundation structures with an enhanced load-bearing capability.
An offshore foundation structure of that kind is known for example from DE 20 2011 101 599 U1 to the present inventor. When such an offshore foundation structure is anchored in the sea bed and a wind power installation is fixed thereto it may be necessary to maintain same. For maintenance of the wind power installation fitters are taken by means of a boat to a landing structure, a so-called boat landing, and from there the fitters have to climb upwardly to up to 22 metres by way of a substantially vertically extending ladder in order to get on to the platform, the so-called working platform, which extends at the interface, the so-called transition piece. A small recovery platform is usually provided at about halfway up the ladder so that the fitters do not have to climb the entire distance in one go but can take a rest at an intermediate point. Nonetheless the climbing operation is greatly exhausting and particularly in the case of older or unaccustomed workers leads to serious physical problems. In addition climbing over the open sea is very dangerous, also because the fitter is constantly exposed to wind and water while climbing the ladder.
It has therefore already been proposed that the ladder be replaced by an elevator which goes directly from the boat landing to the working platform. Admittedly it is possible in that way to avoid the physical exertions which occur when climbing up the 22 metre-long ladder, but an elevator is costly and susceptible to trouble. In addition it is usually necessary in the case of such offshore support structures to provide more than one ladder or elevator so that, depending on the weather conditions, the support structure can be approached with the boat from different sides.